The numbers cited in there don't make sense. Something has to have been garbled from the original research report. The article says:

The farms are inefficient, producing just one kilogram (2.2 pounds) of shrimp for 13.4 square kilometers (five square miles) of mangrove

But Asian shrimp farms produce over a million tons of shrimp per year:

http://www.shrimpnews.com/FreeReportsFolder/NewsReportsFolde...

If it takes 13.4 square kilometers of mangrove per kilogram of shrimp, Asian shrimp farms would occupy more than

13.4 * 1000 * 1000000 = 13,400,000,000

(13.4 billion) square kilometers of mangrove. That's about 26 times the surface area of Earth.